“Redshirting is the practice of holding a child back for an extra year before the start of kindergarten, named for the red jersey worn in intra-team scrimmages by college athletes kept out of competition for a year,” Maria Konnikova reported Thursday. “ Many parents decide to redshirt their children not because they seem particularly immature or young but because they hope that the extra year will give them a boost relative to their peers.

“The data, however, belies this assumption. While earlier studies have argued that redshirted children do better both socially and academically — citing data on school evaluations, leadership positions and test scores — more recent analyses suggest that the opposite may well be the case: the youngest kids, who barely make the age cutoff but are enrolled anyway, ultimately end up on top — not their older classmates.”

“We find that exposure to more mature kindergarten classmates raises test scores up to eight years after kindergarten, and may reduce the incidence of grade retention and increase the probability of taking a college-entry exam,” Cascio and Schanzenbach wrote. “These findings are consistent with broader peer effects literature documenting positive spillovers from having higher-scoring peers and suggest that — contrary to much academic and popular discussion of school entry age — being old relative to one’s peers is not beneficial.”

Konnikova’s explanation for why she placed so much weight in the findings of Cascio’s and Schanzenbach’s paper: “Their approach differed from most studies of redshirting in one crucial way: the students had been assigned totally randomly to their kindergarten classrooms, with no option for parents to lobby for, say, a different teacher, a different school, or a class in which the child would have some other perceived or actual relative advantage. This led to true experimental variation in relative age and maturity. That is, the same student could be relatively younger in one class, but relatively older in another, depending on his initial class assignment.”

A 2011 post on the Freakonomics blog illustrates the rationale behind the theory Konnikova attempts to debunk — namely, that children who are relatively older than their peers will parlay that age advantage into higher achievement.

“Children who are a few months older than their peers at 5 or 6 have more developed cognitive and motor skills, which makes them more advanced athletes and students,” the Freakonomics staff wrote. “This early advantage can lead to self-fulfilling prophecies later on: The child thinks she is an underachiever, and so will often play that role.”